1. Field of the Invention
This invention relates to air classifiers for separating coarse and fine fractions of solid material and more particularly refers to a new and improved circulating air classifier with vertical axis in which the air blower is located outside the classifier separator and air containing fine material is transferred from the classifier separator to separating cyclones and the cleansed air recirculated to the blower.
2. Description of the Prior Art
A vertical axis air classifier is one in which the rotating components are carried on a vertical shaft. In a circulating air classifier with vertical axis, the sifting or classifier air is moved by a blower outside the separator housing. The material to be separated is fed to a rotating spreading disc within the separator chamber, which throws the material to be separated into the separator chamber and thereby spreads it uniformly in veil-fashion over the entire separator area, so that the air stream helically rising in the separator chamber can seize the dust to be separated as completely as possible and remove it from the separator chamber. Under the influence of centrifugal and gravity forces, the coarse matter leaves the separator chamber in a downward direction via a collecting funnel.
In this classifier, all the material to be separated is conducted into the separator chamber. This is a disadvantage particularly if the material to be separated has percentagewise fewer fine components than coarser material. As a result, the separator chamber is unnecessarily loaded, whereby the efficiency of the separation process is adversely affected. Thus, it is most difficult if not impossible to separate the coarse matter sharply from finer material in the feed material undergoing classification. This factor of sharp separation of the coarse matter, however, is important for the production of flour-free grit, if the latter is to be returned to a mill for further grinding. The coarser grains also cause heavy wear at the spreading disc and at the blades of the centrifugal system arranged above the spreading disc.